This application is based on and claims the benefit of European Patent Application No. 00401342.1 filed May 16, 2000, which is incorporated by reference herein
The invention concerns an optical cable having at least two optical fibers, composed of plastic, which are surrounded by a common sheath made of insulating material, e.g., as described in published German application DE 43 36 643 A1.
Optical fibersxe2x80x94referred to in the following as OFxe2x80x94made of glass or plastic are used more and more in communication technology in place of metallic conductors for the transmission of signals. OF composed of glass are overwhelmingly used for longer transmission paths of, for example, more than 2 kilometers. OF composed of plastic are particularly suitable for shorter transmission paths. Polymers, for example, such as polymethylmethacrylate or polycarbonate, are used as materials for these OF. Both types of OF are mechanically sensitive. They must particularly be protected against radially acting forces and against bending around radii which are too small.
An optical cable is described in DE 43 36 643 A1, mentioned above, with two OF composed of plastic which are positioned in a protective sheath. The protective sheath comprises a metal band formed into a tube and a polymer sheath layer applied externally to the tube. The OF are thus to be protected against moisture and aggressive media, as well as high temperatures. If such a cable is, for example, bent and repeatedly stretched as a flexible cable in a drag chain, the OF can quickly become no longer usable for signal transmission.
It is an object of the invention to make the optical cable described above in such a way that its functionality is retained even with frequent bending and stretching.
This object is achieved according to the invention in that,
the OF are stranded together with a short length of lay, which is smaller than six times diameter of an OF,
at least two layers of high tensile strength fibers composed of insulating material are stranded around the OF, which are stranded together, and
the sheath is located over the high tensile strength fibers.
Merely the short length of lay with which the OF are stranded together makes the optical cable as a whole very bendable and stretchable multiple times, with the transmission properties of the OF remaining nearly unchanged for a long time. Through the additional application of at least two stranded layers of high tensile strength fibers over the OF, which are stranded together, overall an optical cable with OF composed of plastic is made which indefinitely retains its transmission properties without restrictions, even if it is constantly alternately bent and stretched, for example during use in a drag chain.
Advantageous developments of the invention will be clear from the detailed description and claims below.